1. Field of the Invention
The present invention relates to a pipe member for forming a main beam such as a steering hanger beam for use in, for example, an automobile, and, in particular, to a pipe member of which the part in the longitudinal direction forms a large diameter section of a multiple pipe structure to improve strength and to lighten.
2. Description of the Prior Art
FIG. 10 is an exploded perspective view showing one example of a steering hanger beam for a conventional right-hand drive car. The steering hanger beam is a member provided in the lateral direction of an automobile to mount an instrument panel on a body. The steering hanger beam is, as shown in FIG. 10, constructed by mounting various kinds of brackets or the like on a pipe member forming a main beam.
The pipe member forming the main beam is, as shown in FIG. 11, constructed from a single pipe of the same material, outer diameter, and thickness (e.g. carbon steel for machine structural use, outer diameter of 60.5 mm, and thickness of 2 mm). This pipe is made of a metal such as carbon steel (STKM) for machine structural use or aluminum.
There is also a case where a pipe member is used for which the diameter is expanded only on the driver""s seat side, where strength and rigidity are required, to have a larger cross-section. For example, Japanese Unexamined Patent Publication No. HEI 8-58432 discloses reinforcement for an instrument panel which is provided with a thick and large diameter section for supporting steering on the driver""s seat side, a thin and small diameter section for supporting interior parts on the passenger seat side, and a tapered section for connecting the large diameter section to the small diameter section. Japanese Unexamined Patent Publication also discloses a hollow stepped pipe for producing the reinforcement and a production method for the reinforcement.
Further, as a pipe member for forming the main beam, as shown in FIG. 12, a pipe member of a split type formed by joining two kinds of pipes with different material, outer diameter, and thickness by welding is used. For example, a pipe A made of carbon steel for machine structural use (JIS G 3445 STKM11A) of an outer diameter of 42.7 mm and a thickness of 1.2 mm is used on the passenger seat side. A pipe B made of carbon steel for machine structural use (JIS G 3445 STKM13B) of an outer diameter of 60.5 mm and a thickness of 2 mm is used on the driver""s seat side. An end of the larger diameter pipe B is processed by drawing to allow the outer diameter to agree with the pipe A of a smaller diameter and both pipes A and B are then joined by arc welding or the like.
In the pipe member of an integral type shown in FIG. 11, the material, outer diameter and thickness are determined according to a section where strength and rigidity are most required. Accordingly, there is overspecification for such a section where strength and rigidity are not required, resulting in overweight. The manufacture of the pipe member of the split type shown in FIG. 12 is highly costly because of the joint.
In recent years, performance required for the steering hanger beam has become higher because of safety measures when automobiles collide. As a result, many parts are incorporated to satisfy desired values. Thus, the total weight of the steering hanger beam has increased. It is therefore desirable that strength and rigidity necessary for each section such as the passenger seat side and the driver""s seat side be secured and the pipe member forming a main beam be lightened.
It is therefore an object of the present invention to solve the above-mentioned problems and to provide an improved pipe member which can secure strength and rigidity required for each section and lighten the pipe member by partially making the pipe member a multiple pipe structure (including a double pipe structure) and integrally expanding the diameter of this multiple pipe structure section using a pipe expansion technique.
To solve the problems above, in a pipe member according to the present invention, engaged with or press-fitted to the outside of a metal pipe is a metal pipe of a larger diameter than the former. In this manner, a multiple pipe structure is formed in a predetermined area in the longitudinal direction and the diameter of this multiple pipe structure section is integrally expanded.
By making a predetermined section of the pipe member a multiple pipe structure, it is possible to allow each section to have the necessary strength and rigidity. By expanding the diameter of part or all of the multiple pipe structure section, it is possible to integrally join the pipes without welding. Since a section where high strength is not required is provided with a pipe of a smaller diameter, it is possible to lighten the pipe member.
Since an end of the multiple pipe structure section or a section close to that end is provided with a tapered section where the amount of diameter expansion gradually increases, it is possible to prevent the strength at this section from suddenly changing. Further, since the small diameter metal pipe can have a different material from the large diameter metal pipe, it is possible to obtain the strength necessary for each section. Still further, if one metal pipe forming the multiple pipes is made of aluminum, it is possible to further lighten the pipe member.
The pipe member according to the present invention is also applied to a main beam of a member for mounting an instrument panel. By engaging or press-fitting a metal pipe of a larger diameter to a metal pipe of a smaller diameter extending from the driver""s seat side to the passenger seat side to provide a multiple pipe structure on the driver""s seat side and by integrally expanding the diameter of the multiple pipe structure section, it is possible to allow each section of the driver""s seat side and the passenger seat side to have necessary strength and rigidity and also to lighten the pipe member.
Referring to other pipe members according to the present invention, if a metal pipe with substantially the same diameter is press-fitted, while reducing the diameter, to the inside of the metal pipe of which the outer circumference is put under control, a multiple pipe structure section is integrally formed. By having such a construction, it is possible to easily produce pipes similar to a piece of pipe that has parts with different thicknesses.
Further, by expanding the diameter of the multiple pipe structure section from inside, it is possible to improve the strength of the multiple pipe structure section.
As described above, one metal pipe forming the multiple pipes can also be of another metal pipe such as aluminum or the like to lighten the pipe.